xxIRT (version 2.0.0)

irt.model.3pl: 3-parameter-logistic Model

Description

irt.model.3pl creates a 3PL irt.model object

Usage

irt.model.3pl(people = NULL, items = NULL, responses = NULL)

Arguments

people

a data frame of theta parameters

items

a data frame of a, b, c parameters

responses

a data frame of dichotomous responses

Value

a irt.mode object

Details

All arguments in irt.model.3pl are allowed to be NULL. If not NULL, (a) the people argument is expected to be a data frame with a column named theta, the items argument is expected to be a data frame with three columns named a, b, and c, and the responses argument is expected to be a data frame with dimesions equal to the numbers of people (in rows) and items (in columns).

Examples

# create a 3pl model with manual inputs
people <- data.frame(theta=c(-1,0,1))
items <- data.frame(a=c(.5,1,1.5,1,1,1,1), b=c(0,0,0,-1,1,0,0), c=c(0,0,0,0,0,.1,.2))
responses <- data.frame(item1=c(0,0,1), item2=c(0,1,1), item3=c(0,1,1), 
item4=c(1,1,1), item5=c(0,0,1), item6=c(0,1,1), item7=c(1,1,1))
x <- irt.model.3pl(people, items, responses) 
x$probability(x)
x$information(x)
x$likelihood(x)
# create a 3pl model with generated data
x <- irt.model.3pl()$gen.data(10, 5)
x$probability(x)
x$information(x)
x$likelihood(x)